Muscle memory kicks in, a soothing response set against a familiar whirling backdrop of sounds and images. It must have been like that last Sunday in Kansas City for Chiefs coach Romeo Crennel, linebackers coach Gary Gibbs and general manager Scott Pioli. It must have sometimes seemed rather normal.

Adrenaline kept them from being frozen, from crumbling to their knees and sobbing hysterically. Barely 24 hours earlier they had been at the vortex of an experience so severe, so incomprehensible, its emotional and physical repercussions might not ever completely vanish.

But in the immediate gloom, they soldiered on, they pulled up their bootstraps—pick your cliché. They did what others have been forced to do after witnessing the unfathomable.

Four years ago, there was Jaromir Jagr, blithely discussing a shift change with his teammate Alexei Cherepanov when Cherepanov suddenly collapsed on the bench, right into Jagr, during a hockey game in Russia and died soon after. Jagr later said that not often, but now and then, when something about the mood of the moment feels familiar, he could sense Cherepanov’s energy near him. It’s a comforting feeling, Jagr said, but then he shook his head and didn’t want to speak about it anymore.

There were the Minnesota Vikings on a brutally scorching August day in 2001, gathering in a panic around lineman Korey Stringer as he fell unconscious and later died of heatstroke. They had been practicing in full pads and helmets, as the heat index reached 110 degrees. Lawsuits were filed; the NFL was forced to change certain macho training camp procedures that could have been at fault just as surely as the stifling conditions.

There’s a would-be jockey out of Ireland who found himself carrying around a woman’s hand that he retrieved in the steaming ruble left by the decimated Twin Towers following the Sept. 11 terrorist attacks. In an NFL game back in 1971, there was a Detroit wide receiver named Chuck Hughes who ran a deep pattern and then, while jogging back to the huddle, dropped dead of a heart attack, right in front of Dick Butkus. All these years later, Butkus still can’t talk about it.

Most anyone who was at the track in Daytona Beach on that chilly February day in 2001 will never fully shake the sound (“like a tiny part of the world exploded,” said Laurie West, who stood near one of the pits) or forget the awful smell (“death and gasoline”) that arose from the final lap of carnage that took the life of Dale Earnhardt. A decade on, some of the same souls watched in horror as Dan Wheldon’s IndyCar flew high into the catch fence, another great one gone.

Cataclysmic events rarely announce themselves. Pioli initially had no idea why Jovan Belcher was at the team’s practice facility Saturday morning, but then Pioli saw Belcher had a handgun. Just minutes earlier Belcher, a fourth-year linebacker, had killed his girlfriend, 22-year-old Kasandra Perkins, in a domestic dispute, shooting the mother of this 3-month-old daughter nine times with a different gun before making the 10-minute drive to the stadium.

Soon, Crennel and Gibbs joined Pioli in the parking lot, and the three begged Belcher to put down the gun. Belcher, according to the Chiefs, thanked the men for all they had done for him as an undrafted free agent, but after hearing police arrive, he moved behind a vehicle, dropped into sports' familiar one-knee pose, and fired one fatal shot to his head.

Crennel has promised he’ll never fully discuss publicly what he observed in that parking lot. Those who know him say he’s spent the last few days in a manic mode, barely sleeping as he rushes around trying to make sure his players and staff have the support they need, that they’re eating, talking, sharing, breathing.

He’s a well-meaning caretaker, a coach who has forced himself to take on extraordinary duties in this time of crisis. But who’s caring for him? On that fateful Saturday morning Pioli, according to Sports Illustrated, called Crennel on his cell phone at the request of Belcher, who wanted his coach and Gibbs to come outside. If that is true, imagine the awful running loop in Pioli’s head about how he beckoned two colleagues to an area where a man with a gun was coming undone.

Trauma’s evil sidekick is known to bombard the mind with disturbing images as the person continually re-experiences the terror of the original event. Those raging thoughts, emotions and physical sensations can become imprinted on the psyche, making it difficult to release feelings of helplessness, anxiety or panic. This is just one facet of post-traumatic stress disorder (PTSD). Folks in the sports world aren’t any more immune to it than veterans of war or victims of crime.

Pioli, Crennel and Gibbs will receive mandatory counseling provided by the NFL that could last three months or longer, if needed. Voluntary counseling is also available for the players.

Crennel is the son of a strict career Army man who woke his kids at sunrise with the blare of an air bugle’s “Reveille,” and taught them to pull the bed sheets as tight as skin on an apple if they wanted to have breakfast. So enraptured by his father Joseph—everyone called him Sarge—Crennel enrolled in the ROTC program at Western Kentucky University with aspirations of becoming an Army sergeant himself, before flat feet and a bit of a belly forced him to choose coaching, where his military training could still be of use.

The military code is slowly evolving, but its ethos is sometimes difficult to break. Feelings aren’t easily shared. Pain, in its many forms, gets blocked.

And barracks have much in common with sports locker rooms and firehouse kitchens. There sit men (and some women) doing their damn best to navigate emotions. Psychologists and counselors can offer the textbook way to handle witnessing a tragedy, but it doesn’t hurt to hear from those who bear the scars.

Sean Cummins was a budding apprentice jockey in Dublin when he first saw someone die. A young man stepped out of a truck directly in front of a car. Cummins was eight, and nearly 42 years later he can describe that moment to you in vivid color if you so wish. A few years on, he saw another person killed when they were hit by a horse and later, when he moved to the States and became a New York City firefighter, he says he went through a dark period where every 24 hours he’d see another dead person. There was a crane accident with seven fatalities, a man who had a heart attack on a plane in which Cummins was a passenger, a girl in a car wreck who still haunts him.

Now Cummins is speaking from his basement in Rockaway Park, Queens, where he says water that "reached 5 feet, 7 1/2 inches" from Superstorm Sandy destroyed “everything I own, 99 percent of it is gone. Everything I brought over from Ireland, everything I brought back from Iraq, I lost my car, lost my motorcycle, it was my only toy.”

Fittingly, one of his lone salvageable tokens is a framed picture of his face superimposed on a box of “Unlucky Charms,” a gift from mischievous fellow firefighters. It makes him chuckle, still.

Cummins became an American citizen in 1989, when he joined the US military reserves, and was a member of the elite FDNY Squad 1 that lost 12 men during the Sept. 11 attacks. He was supposed to be on duty that morning but switched because his mother was flying back to Dublin. In effect, two men covered for him, and both died.

“So I have the dubious honor of killing two people,” he says, repeating a line he has heard hundreds of ways around the kitchen table, gallows humor that keeps everyone from scrutinizing the dregs in their coffee cups.

For three straight weeks he worked on the pile downtown, crawling into tight spaces filled with things he still can’t mention, convinced he might find his friends’ helmets or scraps of their existence. For a while he walked around the ruins with a woman’s hand, an act that made sense to his wounded mind back then.

“One of the reasons I went to Iraq was my own punishment. If my friend gave a life, I could give a year,” says Cummins, who recently retired from the military reserves after 22 years but is still with the FDNY, having moved to the prestigious Rescue Company 1.

Diagnosed with PTSD, he says he “couldn’t function at home” after 9/11. “We got forced to sit down and talk with psychologists, but it’s the black humor that got us back to being somewhat whole," he says. "Everybody that breaks my chops, not one of them means it. It gets talked out in the kitchen, it’s a ball-breaking session. ‘Oh, you killed two guys.’ I can take it, I can even smile about it.

“You think of those coaches in Kansas City, they’re going to need that bond. They’re going to need people they know and trust to sit and talk with them. Guilt is a powerful force. It can really mess you up. You fly on adrenaline, doing whatever you can to forget, and then it hits and it can get really bad.”

Visions might always linger, what-ifs may never be answered. Jagr has the wafts of energy that sometimes nudge him, Moss has the friend who never really left. Witnesses to tragedy and death move on, carrying what they choose.